Method of making shielded spark plug connectors



May 16,1944. T. w. MILTON METHOD OF MAKING SHIELDED SPARK PLUGCONNECTORS Filed April 6, 1942 I h/ H 5f. Z

INVENTOR 20/1145 )/2 BY f M,

ATTORNEY V Patented May 16, 1944 METHOD OF MAKING SHIELDED SPARK PLUGCONNECTORS Thomas W. Milton, Detroit, Mich., assignor to The Flex-O-TubeCompany, a corporation of Delaware Application April 6, 1942, Serial No.437,746

4 Claims.

ing such intimate contact irrespective of elongation or contraction ofthe spark plug and connector elements incident to a wide variation oftemperature conditions encountered in practice.

A further object is to provide a spark plug connector including such ayieldable element and means for preventing the portion which makescontact with the ignition lead conductor from puncturing the latter andits insulation to such an extent that it will then puncture theconnector body and cause electrical leakage or shortcircuiting.

Another object is to provide a spark plug connector with a radioshielding envelope which has no mechanical functions, in other words,the insulating body of the connector mechanically carries the load ofconnection to the spark plug and to the ignition lead shielding.

A further object is to provide a spark plug connector by amethod whichinvolves first moulding the insulating body, then plating the radioshielding thereon, then securing shield connections or connectionelements to the body, and then completing the electrical path betweensuch connection elements and the shielding for such connector body.

For the purpose of illustrating the genus of the invention, a typicalembodiment is depicted in the accompanying drawing, in which:

Fig. 1 is a central vertical section taken through a spark plug, aconnector therefor, and a portion of an ignition conductor which leadsinto such connector.

Figs. 2 and 3 are transverse sections taken through the connectorsubstantially on the line 2-2 and 3-3 of Fig. 1.

Referring to the drawing, the spark plug comprises a body shell 10,threaded externally as indicated at H for engagement with an appropriateopening in a cylinder wall. The outer end of the shell Ill is providedwith an electrode piece I! and the inner end of the shell is internallythreaded as indicated at l3 to receive the lower end of a retainingsleeve l4.

Disposed within the lower half of the retaining sleeve l4 and within theshell I0 is a center electrode l5 having a tip 16 formed with a shoulderl1. Disposed about the electrode 15 is a mica or like tube l8 providedwith a shoulder 20 adapted to cooperate with the lower, end of retainingsleeve 14. The retaining sleeve M is internally recessed or cored outthroughout the major portion of its length beginning from its upper orinner end as indicated at 2| to receive a ceramic insulating sleeve 22which is cemented to the mica tube l8 by alayer of heat resistant cement23. The upper end of the electrode I5 is provided with a partiallyspherical depression 24 and the metal at the extremity of electrode l5adjacent such depression is swaged over a washer 26 disposed at theupper end of the mica tube I8 to fix the parts of the plug in assembledrelationship. The upper end of the retaining sleeve I4 is externallythreaded, as indicated at 21, to receive a spark plug nut 28.

The spark plug connector comprises a moulded plastic elbow 30 formedunder conditions most favorable to moulding operations so that the elbowwill have of itself the requisite mechanical strength. The elbow body3|! is provided with bores 31 and 32 intersecting at a suitable desiredangle as illustrated in Fig. l, the bore 3| being adapted to receive anignition lead 33 and the bore 32 to receive up to a shoulder 34 aceramic insulator and spring guide 35.

A contact spring 36, preferably of a copper beryllium alloy, as pointedin 31 and 38, the end 31 being adapted to pierce the insulation ofignition lead 33 and point 38 being adapted to make positive contactwith the upper end of electrode l5 within the partially sphericaldepression 24. The contact spring element 36 is further provided with anumber of active coils 40 disposed between the lower end of the ceramicinsulator 35 and the upper end of the center electrode I5 so that withthe elbow 30 in assembled relation with respect to the spark plug, thesecoils remain in compressed condition and force a straight portion 4|disposed within the ceramic insulator 35 upwardly so that the point 31of this straight portion just pierces the conducting wires of ignitionlead 33 without projecting through the insulating layer of lead 33 whichlies above the conducting wire thereof. It is noted that the insulatingelement 35 abuts shoulder I4 or the elbow body 30 so that point I!cannot be driven upwardly so asto puncture the insulation of lead wire33 which lies above the conducting wires and cannot puncture the plasticmaterial of elbow 30 above the ignition to a thickness of from one toone and one-half thousandths in thickness... Threads 4! are provided atthe ends of the ignition wire and spark plug branches of elbow 30 andfittings 44 and 45 are threaded thereon. The fittings and 48 areanchored to the plated radio shielding 42 by first cleaning the portionof the radio shielding which is to be covered by portions of thefittings 44 and 46, then wrapping the ends of the shielding with a fluxsolder foil, then threading the fittings onto the elbow until the solderfoil is compressed between the fittings and the radio shielding, thencrimping the fittings centrally at the foil, and then completing thesoldering by locallzed heat.

It is noted that the lower end of the fitting 4| is internally threadedas" indicated at 4G to receive a flanged bushing 41 with an inturnedflange 48 of spark plug nut II arranged on the bushing between itsflange and the lower end of fitting 45. The threaded connection betweenthe fitting 45 and the fianged bushing 41 is preferably soldered orbrazed to prevent disconnection of these parts. The fittings 44, 45,electroplated shield 42, bushing 41, spark plug nut 28, retaining sleevel4 and spark plug body l provide a complete radio shielding over thespark plug connector and spark plug, such shielding being grounded tothe spark plug body ill.

As many changes may be made in the above described construction and manyapparently widely difl'erent embodiments of this invention could be hadwithout departing from the spirit and scope thereof, itis intended thatall matter contained in the above description or shown in theaccompanying drawing shall be interpreted as illustrative and not in alimiting sense.

I claim:

1. The method of making a radio shielded spark plug connector body whichconsists in molding a plastic body having ignition wire and spark plugbranches, then electroplating said body, forming threads in the plasticbody free end portions of said ignition wire and spark plug branches,threading fittings on said threaded branch ends of said plastic bodywith solder interposed between the fittings and the plating on saidbody, inwardly compressing the fittings at points over the solder, andcompleting the soldering by local applications of heat.

2. In the manufacture of a radio. shielded spark plug connector body,the steps of molding a body of non-metallic plastic material of thedesired size, shape and contour, applying an enveloping metallic coatingto the exterior surfaces of said body by an electro-plating process,forming threads in said material at an end of said body, threading ametallic threaded connector member on said threaded end of said body,then metallically bonding said metallic connector member to saidcoating, and mechanically interlocking said connector to said body.

3. In the manufacture of a radio shielded spark plug connector body, thesteps of molding a nonmetallic plastic material to the desired size,shape and contour of the desired body, subjecting said body to anelectro-plating process whereby to apply an enveloping metallic coatingto the exterior surfaces thereof, forming threads in said material on anend of said body, threading a connectors to said body to preventrelative rotation between them, and

metallically bonding said threaded connectors to said coating.

THOMAS W. MILTON.

